It's basically a form of post modernism where the concept of a separate civilization is being diluted on purpose. In Civ 8/9 by endgame all borders will be erased and replaced with new economic zones as "social movements" and corporations replace governments..... and I only half joke about this cause I can see it happening. Rip Civilization long live Civilization.
Basically, the Civ games have always played fast and loose with the words 'Civilization', 'State', 'Nation', 'Government', and 'People', and that is making for some issues when they change the relationship between these things. This is not post-modernism, though. That is an entirely different concept.
The fact that states have always been made up of multiple ethnicities (also called nations, or tribes, depending on size), and that their ethnic makeup changes over time is not a post-modern idea. However, during the formation of the modern world, it was often rejected during the reification of the nation-state - a state that is made up of one nation (ethnicity). It is true that in recent years this has moved, in history, from a somewhat controversial position to the standard one, but this is not post-modernism. Post-modernism is very hard to define, since it is in part about rejecting grand narratives and definitions, but it's definitely not what happened after modernity. The only academic historians I know of who maintain that states are, and should, be made of one nation are those who sell themselves for views and book sales. Grifters, basically. But this has come at a time where some academically accepted facts are controversial in some places, and Civ 7 has definitely caught the ire of some 'historians' who would also reject the multiple nations within Rome, Greece, Assyria, Russia, China, Japan, England, America, France, Spain etc etc.
With Civ 7, Civ has become
more historically accurate. BUT it's not necessarily explaining that well, with them describing switching Civilizations rather than the well-documented process of one nation rising in power within a state, and describing it as an abrupt change rather than a period of flux.
A big problem is that they have to time-skip at least some amount, because the nations within your state are not simulated in the game. I think they skip too much time, and the cut-scene and info screens between eras should be much more detailed about the historical processes they're trying to simulate.
'With the fall of the Empire, your people stopped thinking of themselves as Roman, and the wealth and prosperity of the Abbasids made them rise from a minor part of the Empire to the most powerful nation...' Except that the next part needs to be a fictional fusion of the real histories of Rome and the Abbasids, requiring more reading than almost anyone wants to do between parts of a game, and requiring more writing than Firaxis can do, since they can't even do bugfixes and updates well right now.
At a minimum, they need a bespoke transition narrative between each Civ change,
even from The Normans to the French. Then maybe people would accept era changes.
